1. The Field of the Invention
The present invention relates to wireless networks, and more specifically, to using directional antennas to mitigate interference in wireless networks.
2. Background and Relevant Art
Computer systems and related technology affect many aspects of society. Indeed, the computer system's ability to process information has transformed the way we live and work. Computer systems now commonly perform a host of tasks (e.g., word processing, scheduling, and database management) that prior to the advent of the computer system were performed manually. More recently, computer systems have been coupled to one another to form both wired and wireless computer networks over which the computer systems can communicate electronically to share data. As a result, many tasks performed at a computer system (e.g., voice communication, accessing electronic mail, electronic conferencing, web browsing) include electronic communication with one or more other computer systems via wired and/or wireless computer networks.
For example, a number of computer systems can be coupled to a data hub through corresponding wired connections (e.g., category 5 cable) to form a wired network (e.g., an Ethernet segment). Similarly, a number of wireless computer systems (commonly referred to as “stations”) can be coupled to a wireless access point (“AP”) through corresponding wireless connections (e.g., resulting from appropriate communication between radio transmitters and receivers) to form a wireless network (e.g., an IEEE 802.11 network). Further, a data hub and/or an AP can be connected to other data hubs, APs, or other network devices, such as routers, gateways, and switches to form more complex networks (including both wired and wireless connections).
When computer systems communicate electronically, electronic data will often pass through a protocol stack that performs operations on the electronic data (e.g., packetizing, routing, flow control). The Open System Interconnect (“OSI”) model is an example of a networking framework for implementing a protocol stack. The OSI model breaks down the operations for transferring electronic data into seven distinct “layers,” each designated to perform certain operations in the data transfer process. While protocol stacks can potentially implement each of the layers, many protocol stacks implement only selective layers for use in transferring electronic data across a network.
When data is received from a network it enters the physical layer and is passed up to higher intermediate layers and then eventually received at an application layer. The physical layer, the lower most layer, is responsible for converting electrical impulses, light, or radio waves into a bit stream and vice versa. On the other hand, when data is transmitted from a computer system, it originates at the application layer and is passed down to intermediate lower layers and then onto a network. The application layer, the upper most layer, is responsible for supporting applications and end-user processes, such as, for example, electronic conferencing software, electronic mail clients, web browsers, etc.
An intermediate layer incorporated by most protocol stacks is the Data Link layer. The Data Link layer decodes data packets (received from higher layers) into bit streams for use by the physical layer and encodes bit steams (received from the physical layer) into data packets for use by higher layers. A sub-layer typically included in the Data Link layer is the Media Access Control (“MAC”) layer, which implements protocols for moving data packets onto a shared channel (e.g., an Ethernet segment or an IEEE 802.11 channel).
However, to access a medium a computer system must be able to sense the medium. In a wireless environment, sensing a wireless medium (e.g., an IEEE 802.11 channel) can be difficult, and at times impossible, depending on how a station and an access point are physically separated. Access points typically include an omni-directional antenna that essentially results in spherical region around the access point. When a station is within a particular range of the access point (e.g., within the spherical region), the omni-directional antenna enables the access point to meaningfully send data to and receive data from the station. That is, within the particular range, transmitted radio signals have sufficient signal strength such that a physical layer can convert the radio signals into a bit stream.
Many wireless devices communicate in unlicensed frequency bands (e.g., in the 2.4 GHz band). Communication between wireless devices operating in unlicensed bands can be degraded do to transmissions from other devices that operate in the same unlicensed band. For example, some cordless telephones, some microwaves, BlueTooth devices, a wide variety of control devices, and IEEE 802.11b devices all operate in the 2.4 GHz band. Thus, cordless phones, microwaves, BlueTooth devices, and control devices (hereinafter referred to as “interfering devices”) can interfere with communication between an IEEE 802.11b station and an IEEE 802.11b access point.
IEEE 802.11b effectively has three channels that can be used for communication between an IEEE 802.11b access point and IEEE 802.11b station. Thus, when there is increased interference one IEEE 802.11b channel, interference can potentially be reduced by switching to another IEEE 802.11b channel. However, since there are effectively only three channels, it is often difficult, if not impossible, to find a channel that has reduced interference at every location within a spherical region surrounding an IEEE 802.11b access point. A first channel may have increased interference on one direction, a second channel may have increased interference in a second direction, and a third channel may have increased interference in a third direction. Unfortunately, as typically implemented an omni-directional antenna can only be tuned to one channel at a time. Thus, if an IEEE 802.11b station is located in each of the first, second, and third directions, there would be virtually no way for an omni-directional antenna to select a channel such that each IEEE 802.11b station could communicate with reduced interference.
Interference from interfering devices can degrade the speed and reliability of data transferred between an IEEE 802.11b station and an IEEE 802.11b access point. For example, interference from an interfering device at or near an IEEE 802.11b station can cause the IEEE 802.11b station to communicate at a significantly reduced data rate (and, if the interfering device has high gain, potentially make communication impossible). Further, when an interfering device is at or near an IEEE 802.11b access point, communication with a number of associated IEEE 802.11b stations can be degraded. Signal degradation due to interference may result in an omni-directional antenna being able to detect that radio waves are being received but may make it impossible to determine what data is being represented by the radio waves. That is, a physical layer may not be able to generate a bit stream from the degraded radio waves. Therefore systems, methods, and computer program products for mitigating the effects of interference during wireless communication would be advantageous.